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s imulation Tools Model i cing for a ircraft d esign
nasa t echnology ere’s a simple science experiment to try: Place an unopened bottle of distilled water
H in your freezer. After 2–3 hours, if the water
is pure enough, you will notice that it has not frozen.
Carefully pour the water into a bowl with a piece of ice in it. When it strikes the ice, the water will instantly freeze.
One of the most basic and commonly known scien- tific facts is that water freezes at around 32 °F. But this is not always the case. Water lacking any impurities for ice crystals to form around can be supercooled to even lower temperatures without freezing. High in the atmosphere, water droplets can achieve this delicate, supercooled state. When a plane flies through clouds containing these droplets, the water can strike the airframe and, like the supercooled water hitting the ice in the experiment above, freeze instantly. The ice buildup alters the aerodynamics of the plane—reducing lift and increasing drag—affecting its performance and presenting a safety issue if the plane can no longer fly effectively. In certain circumstances, ice can form inside aircraft engines, another potential hazard.
NASA has long studied ways of detecting and counter- ing atmospheric icing conditions as part of the Agency’s efforts to enhance aviation safety. To do this, the Icing Supercooled large droplet conditions caused the buildup of ice on this aircraft. Using the NASA LEWICE software, aircraft Branch at Glenn Research Center utilizes a number of manufacturers can model the ice accretion and the various shapes the ice can form (such as the inset example) on aircraft surfaces.
world-class tools, including the Center’s Icing Research Tunnel and the NASA 607 icing research aircraft, a in icing research and aircraft design and certification. kind of ice would result, and what shape that ice would “flying laboratory” for studying icing conditions. The LEWICE has been transformed over the years from strictly take. Users can enter geometries for specific, two-dimen- branch has also developed a suite of software programs to a research tool to one used routinely by industry and other sional cross sections of an airfoil or other airframe surface help aircraft and icing protection system designers under- government agencies. Glenn contractor William Wright and then apply a range of inputs—different droplet sizes, stand the behavior of ice accumulation on various surfaces has been the architect of this development, supported by temperatures, airspeeds, and more—to model how ice and in various conditions. a team of researchers investigating icing physics, creating would build up on the surface in various conditions. The One of these innovations is the LEWICE ice accre- validation data, and ensuring development according to program’s versatility, ease of use, and speed—LEWICE tion simulation software. Initially developed in the 1980s standard software engineering practices. The program can run through complex icing simulations in only a few (when Glenn was known as Lewis Research Center), provides a virtual simulation environment for determin- minutes—have contributed to it becoming a popular LEWICE has become one of the most widely used tools ing where water droplets strike an airfoil in flight, what resource in the aviation industry.
82 Public Safety Spinoff 2011 “LEWICE is considered the premier code in the world he says, is the years of icing data Glenn has accumulated needed to ensure safe flight. Parkins estimates that using for doing ice-shape generation,” says Mark Potapczuk, using its various research tools. the technology in this process saves American Kestrel’s an aerospace engineer at Glenn who has coordinated the “LEWICE is a unique code in that it has one of the customers hundreds of thousands of dollars in costs by reducing tunnel testing and precluding expensive, late development of the LEWICE code over the years. world’s most extensive validation sets,” he says, explain- stage design changes.
The software is available to U.S. users at no cost from ing that Glenn has used its icing flight test bed and icing “It’s a tool that helps reduce risk substantially and Glenn, and is distributed to everyone from graduate wind tunnel not only to help refine and develop LEWICE provides a lot of confidence that you have a design that is students at universities to multimillion-dollar compa- but to validate the code’s results. “Glenn has some of the going to succeed,” he says.
nies. One such user has capitalized on the capabilities best icing researchers in the world at one of the best icing Glenn continues to evolve LEWICE to address new of LEWICE, developing a toolset with the potential to facilities in the world working on that software, and they areas of icing research, including large supercooled enhance the utility of the NASA-developed software. have evolved it into a very robust tool.” droplets and engine icing. As useful a tool as LEWICE To help design and certify an aircraft or icing p artnership has been, Parkins says, its importance will only continue protection system for flight, manufacturers need to know ublic afety to grow.
how ice accumulates on their particular designs. Through “I execute literally thousands of runs of LEWICE p s “The modern certification process has resulted in air- every year,” says David Parkins, founder and president of using LEWICE or LEWINT in conjunction with tunnel craft that are safer in icing conditions than anything we’ve American Kestrel Company LLC. Based in Ithaca, New and flight tests, engineers can determine the kinds of ice ever developed,” he says. “LEWICE has been a key part York, American Kestrel provides research and develop- shapes that form on their designs in varying conditions.
of that.” v ment and consulting services to aircraft manufacturers How these shapes impact the aircraft’s aerodynamics in the field of aviation safety and icing. Parkins has long helps the engineers determine any design alterations used the NASA software to help his company’s customers design safe aircraft that can meet rigorous certification Ice buildup on airfoils can drastically affect the aerodynamics of an standards for flight in icing conditions. He saw room aircraft, leading to potentially hazardous flight conditions. For a deeper look at Glenn Research Center’s Icing Branch and its study of icing for improvement with the program’s user interface, conditions and countermeasures, scan this code.
however, and began developing tools to facilitate the plot- ting and running of the code. Parkins shared the results with Glenn, and the Center formed a partnership with American Kestrel through a Space Act Agreement, allow- ing the company to distribute LEWICE internationally with the company’s new interface.
Benefits American Kestrel’s LEWICE Interface (LEWINT) combines LEWICE with an enhanced user interface, icing analysis tools, and automated plotting. Since 2007, the company has licensed its LEWINT product to 25 customers for applications including developing certified aircraft and analyzing wind turbines for icing issues.
“Within the United States, every airframer uses LEWICE from Glenn, or LEWINT from American Kestrel,” Parkins says. A key to the technology’s ubiquity, Spinoff 2011 Public Safety 83